Frugivory and seed dispersal by the common gecko Hoplodactylus maculatus

Abstract

Although there are many reports on the effect of gut passage on seed viability, few studies of seed dispersal by lizards have investigated the quantitative and qualitative components of disperser effectiveness. I investigated the effectiveness of Hoplodactylus maculatus, the common gecko, as a seed disperser of some fleshy-fruited native plant species in a coastal habitat on Mana Island, New Zealand. An exclusion experiment was set up on Coprosma propinqua plants to measure the level of frugivory by lizards. Seed dispersal quantity was measured by pitfall trapping geckos and removing seeds from droppings collected. Minimum dispersal distances were measured from traps where seeds were collected to the nearest fruiting plant. Germination success of Coprosma propinqua seeds ingested by geckos was compared with seeds collected directly from plants, both with the flesh removed, and from intact fruit. The effect of gecko microhabitat selection, and resulting seed deposition patterns, on germination success was investigated by placing pots containing Coprosma propinqua seeds in four microhabitats on Mana Island. Lizards appeared to be the major frugivore of Coprosma propinqua fruit in the study site, removing large quantities of fruit. Exclusion of birds had no effect on fruit removal rates, and birds were seldom observed in the study site. Forty percent of gecko droppings collected contained seeds, over 95% of which were from Coprosma propinqua. Common geckos are capable of dispersing seeds well beyond the canopy of the parent plant, with Coprosma propinqua seeds dispersed up to at least 9.3 m. Ingestion of Coprosma propinqua seeds by common geckos had no effect on germination success, with 72% of seeds germinating. Geckos tend to deposit seeds beneath rocks, and these microhabitats appear to be suitable for germination of Coprosma propinqua, with high levels of mean seed germination (73%). These results provide strong evidence that fruit is an important component of the diet of Hoplodactylus maculatus, and that common geckos provide effective seed dispersal for Coprosma propinqua. These findings have important implications for restoration of highly modified habitats such as Mana Island. Only on a few offshore islands are lizard densities similar to those in pre-human times. Restoration of lizard species and their plant food sources to predator-free islands is essential to the conservation of plant-lizard interactions such as frugivory and seed dispersal, and the maintenance of fully functional ecosystems.